In the image forming apparatus of the electrophotographic type, a fixing device for fixing an unfixed toner image, as a fixed image, formed on a sheet is mounted. Here, a heating roller and a heating belt are referred to as rotatable heating members (rotatable fixing members), and a pressing roller and a pressing belt are referred to as rotatable pressing members.
Recently, as the sheet, a sheet containing heavy calcium carbonate as a filler in a large amount has been used. In order to enhance a texture of the sheet, there is a tendency to increase a filling amount of the calcium carbonate for the reason that the resultant sheet has high whiteness, excellent opacity, inexpensiveness, and the like. However, sheet powder (paper powder) principally comprising calcium carbonate and generating on such a sheet is liable to be triboelectrically charged compared with sheet powder principally comprising another filler such as kaolin or talc.
For that reason when the sheet containing calcium carbonate in the large amount passes through a nip, the sheet powder is liable to be electrostatically attracted to a surface of the rotatable heating member. Thus, when the sheet powder is deposited on the surface of the rotatable heating member, toner is gradually accumulated at that portion. When an accumulation amount of the toner increases, there is a liability that the toner is transferred onto the sheet or the like and causes an image defect.
Therefore, in order to solve such a problem, in Japanese Laid-Open Patent Application 2009-103789, a method of using a solid image-printed sheet as a cleaning sheet (hereinafter referred to as a cleaning sheet) has been proposed. Specifically, by using a depositing force between toners (toner particles), the accumulated toner is transferred onto a solid image portion of the cleaning sheet, so that the rotatable heating member is cleaned.
However, even when the solid image-printed cleaning sheet is simply introduced into the nip, there is a limit to a cleaning effect on the surface of the rotatable heating member. This is because the sheet powder deposited on the rotatable heating member generates from end portions of the sheet with respect to a widthwise direction in a large amount. That is, on the surface of the rotatable heating member, the sheet powder accumulates move in both widthwise end sides than in a contact region with the sheet. Accordingly, the both end portions of the rotatable heating member with respect to the widthwise direction cannot be properly cleaned, and there is a liability that it leads to a factor of the image defect.